1. Field of the Invention
The present invention relates to a position control system for allowing a data transducer to trace a data track in a disk storage device, and more particularly to a position control system for a disk storage drive system in which a data transducer can be moved to a selected data recording track at a high speed and controlled to keep its relative position to the data recording track.
2. Description of the Prior Art
As information record/playback apparatuses have remarkably been improved in performance recently, the data transducer position control system is required to be more compact in size and more accurate in operation. The position control system acts as a positioning drive device for allowing the record or playback transducer to trace a reference data track in a magnetic disk storage device or an optical disk storage device. The compactness is required for the purpose of increasing the recording capacity in a given size and the high accuracy is also needed for increasing the track density for mass storage.
Deflection of a data track which occurs during tracking, will be described. In an optical disk storage device, the amplitude of track deflection will be about several tens to some dozen tens of micrometers, considerably greater than the width (about 1.6 .mu.m) of a track to be traced, due to the eccentricity of the center of rotation after replacement of a disk medium and/or the deflection of a rotary shaft of spindle motor for rotation of the disk. In a floppy disk drive (FDD), another kind of track deflection will result from the expansion or shrinkage of a base film of the disk medium caused by heatup in addition to the same track deflection as of an optical disk storage device. In this case, the amplitude of track deflection is smaller than that of the optical disk storage device, and the deflection is some dozen to several tens of micrometers in operation. However, the track deflection will not be negligible when the track is reduced in width for mass storage at a high track density.
For the purpose of minimizing such a track deflection, known data transducer position control systems for disk storage drive system have employed various methods which are described below.
As a first example, there is provided a method in which the deflection of a track is estimated by twice differentiating a signal which is the sum of a tracking error signal and an integration signal obtained by twice integrating an input signal to the driver unit for actuating a data transducer for tracking movement. The estimation signal corresponding to one rotation of the disk is stored in a memory and is then read out during a tracking mode and added to the input signal to the driver unit. With the use of such a resulting signal, the traceability of the data transducer can be improved, for example, as disclosed by U.S. Pat. No. 4,594,622. However, it will be difficult to put this method into practice due to the difficulty of suppressing variations in the integration or noise resulting from the differentiation.
As a second example, there is another method in which by extracting a repeatable signal component from the tracking error signal representing a deviation of the data transducer from the reference data track, a Fourier coefficient of a repeatable frequency is obtained and used to calculate a repeatable error compensation signal. The repeatable error compensation signal is then added to a driver input signal of the data transducer. With the use of such a resulting signal, the traceability of the data transducer can be improved with reference to the track deflection at a disk rotation frequency, for example, as disclosed by U.S. Pat. No. 4,616,276. However, the disadvantages of this method are that the arithmetic operation of Fourier analysis is troublesome and that the suppression of a rotation non-synchronous factor is yet unsatisfactory.
Accordingly, a prior art data transducer position control system for disk storage drive system has problems in that the control of variations and noise generated during the estimation of track deflection is too difficult to be executed in practice or in that the arithmetic operation of a repeatable error compensation signal is troublesome.